Porous pipe has been developed that weeps or drips water along its length. The hose wall is a composite formed of a dispersion of a major portion of prevulcanized elastomer particles dispersed in a continuous binder phase, usually a thermoplastic resin such as polyethylene. Channels or crevices are formed in the wall due to the lack of excess binder and the incompatibility between the binder and the dispersed particles. When the pipe is placed under pressure, the wall expands slightly and water traverses the wall and forms beads or drops on the outside surface which drip to form a continuous line source of water. Porous hose can also be used underground as a line source of irrigation at the root level or around foundations to remove excessive moisture from the soil. Representative patents describing the manufacture of porous pipe are U.S. Pat. Nos. 4,517,316, 4,616,055 and 4,615,642.
Porous pipe is finding increasing use as soaker hose manufactured with or without hose fittings for use in retail do-it-yourself (DIY), lawn and garden and professional landscape and agricultural applications. Porous hose used in outdoor applications is found to weather and become brittle and crack after extended exposure to the outdoor ambient environment. It was believed that the aging was due to ozone in the air and was not caused by incident radiation. It is known that hydrocarbon resins such as polyethylene are degraded by ultraviolet radiation. The radiation can create free radicals resulting in chain scission or the creation of peroxy or other radicals that can degrade the polymer chains. However, it is also known that adding 3 to 5% by weight of carbon black pigment to transparent resins such as polyethylene stabilizes them from attack by ultraviolet radiation. Porous pipe is a composite containing at least 60% by weight of reclaimed rubber particles which themselves contain about 30% carbon black. Therefore, the composite hose already contains about 20% carbon black. The product is opaque. It was believed that this opacity and the high content of carbon black would provide all the ultraviolet absorption that the hose required.